I had my best fe day ever today by concentrating not on the iFCD gauge, but rather the assist gauge, trying to minimize assist as much as possible. My usual multiple short runs historically yield fe in the 40s, but today they were in the 50s, 60s, even the 70s. Anyone else have this experience?
add: i allowed regen to occur enough to maintain the battery at 5 or more bars.

Note to Self: Stay out of assist!

Hi Matt;

Welcome to the mysteries and secrets of high FE of the Gen4 IMA platform!

Stay off of the assist, manage you SoC and your FE will be higher, the battery pack will incur a lower number of discharge/charge cycles (which equals longer life) and you'll be the winner.

Cheers;

MSantos

Less assist means less throttle. I would expect higher numbers without question.

I would also expect much slower acceleration and maybe some irate folks behind you.

Try not to stare at the gauge too much, less you end up in a ditch.

After reading this thread, I tried it on the way home last night-- managing Soc instead of focussing on FE-- and sure enough, saw some improvement in my MPG-- even with all my hills! But it seems like the other trade-off is that accelerating slowly (with little or no assist) takes much longer to reach a speed that allows reasonable glide. Any 'rules of thumb' for how you balance these alternatives?

And regarding the Gen4 IMA, why would having a fully charged SoC tend to reduce milage? I've seen that it seems to discharge more rapidly/readily from high states of charge-- is that because the system won't allow 'silent' regen when the SoC is already high?

thanks, Philip

Philip:

Yes, a slower acceleration rate is the trade-off. And not even a steady and fine tuned foot can always help off-set that either. Using the S mode however can help to a certain extent particularly when we want to stay off the assist and accelerate a little faster.

Even getting a 1 or 2 bar assist once in a while is not that bad provided that we put that energy back in the pack soon after. I prefer to kick the engine into a high LOD value soon after reaching 25 MPG (~40 Km/h) as this will put back some of that energy via hidden regen as well.

Honda implemented/programmed what they call the "assist affinity" to be dependent on a variety of factors - one of which is the SoC. Toyota did pretty much the same on the HSD system as well with similar behaviors. The main reason why the car gets "assist happy" at high SoC is because the NiMH packs do not like to be at either end of the charge spectrum for too long. The happy medium is actually in the 60%-75% zone of the SoC which roughly equates to the flatter (and longer) part of the NiMH charge curve.

Why would "riding the pack" end-up netting you lower FE? Because while doing it you would also be pulling a higher engine RPM along with it.

Also, even though you are using more gas due to the higher RPM, sooner or later you have to put that assist energy back into the pack. Whether you do it through deceleration or a forced regen, the end result is a net energy loss you cannot recover.
So really you get dinged twice. Once for the extra fuel to accelerate at the faster rate and the other to charge the pack needed to replace the energy you used.

All HEV hybrids being sold today exhibit these same attributes and riding the pack on any of them is actually worse than staying off of it. No exceptions.

What does this mean to the average hybrid driver? Not much. Since they are already getting better FE than they would on a non hybrid vehicle.

But for the hybrid driver wanting to get the most out of the platform, the path to FE success means understanding where the losses are and minimizing them as much as possible. The only other things we need that the car cannot provided are: purpose, patience and dedication.

Cheers

MSantos

i'm trying to keep it to 3 bars of assist w/accel from a stop and 1 or 2 bars of assist to accel at speed, which gives me adequate accel w/o too big a drain on soc and keeps the drivers behind me off my tail.
i think a full soc means you're spending lots of time in regen, which is costly, fe-wise.

Note to Self: Stay out of assist!

thanks, MSantos, that makes sense. But may I add a couple of rookie questions? I haven't bought a scangauge yet, though I can see its value. LOD-- load on demand, right? Does gently pulsing the accelerator at speed to shift into a lower gear serve as a 'poor man's' way of achieving higher LOD? I recently re-read Tarabell's great post on hypermiling and I've been playing with this method to good effect.

And continuing with my fearlessness in asking potentially dumb questions, when you mention 'using the S mode', are you actually shifting down, or does this refer to another aspect of optimizing the HCH's performance?

thanks P

went from 46mpg on my last tank to 51.8mpg on this tank, using the assist-avoidance approach. my best tank ever by nearly 5mpg.

Note to Self: Stay out of assist!

Pretty much Philip. LOD is one of the gauge values in the ScanGauge that you can choose to display and gives you a percentage value of the current engine load. The engine load on the HCH-II is also one of the determinant inputs for some of the IMA's assist/regen thresholds. You do need a scangauge to properly monitor it as there are specific values that you ought to watch for.


Yes, indeed. But this shifting down to "S" is strategic in nature and meant to represent the best of the available "all bad" options. You neither ride the S for very long nor do you use it in every circumstance, otherwise you'll step outside the optimal FE envelope. One thing to remember when using the S though, you still strive for the lowest RPMS possible as well as avoiding the assist - press the throttle too hard and the assist comes on anyway - which is not optimal any longer.


Cheers;

MSantos

Nice showing Matt. But guess what?

It gets better as you get better at it as well. Add a few more tricks and it is quite possible to crank out 70-90 MPG (US) city-only commute segments. And if you get many of these... well... you get the point

Cheers;

MSantos